Coroutines in Kotlin v2

Slides from my talk at KyivAndroidDevClub #12, 2017-11-11

Transcript

1. Coroutines in Kotlin Dmytro Zaitsev Team Leader @ Lóhika
2. Blocking VS Non-blocking
4. v1: Sequential fun postItem(item: Item) {
 val token = prepareToken() / / 1
 val post = submitPost(token, item) / / 2
 processPost(post) / / 3
 }
5. v2: Async callbacks fun postItem(item: Item) {
 prepareTokenAsync { token -> / / 1
 submitPostAsync(token, item) { post -> / / 2
 processPost(post) / / 3
 }
 }
 }
6. Callback hell
7. v3: Reactive (Future-based) fun postItem(item: Item) {
 observeToken()
 .concatMap { token -> observePost(token, item) }
 .subscribe { post -> processPost(post) }
 }
8. v4: Coroutines fun postItem(item: Item) = launch {
 val token = prepareToken() / / 1
 val post = submitPost(token, item) / / 2
 processPost(post) / / 3
 }
 }
9. Experimental status Kotlin 1.1 -Xcoroutines=enable kotlin.coroutines.experimental -> kotlin.coroutines
10. Experimental status New style of programming The design is not final and expected to change JetBrains still collects information and feedbacks Can and should be used in production Backwards compatibility guaranteed
11. Terminology coroutine suspending function suspending lambda suspending function type coroutine builder suspension point continuation
12. Terminology coroutine suspending function suspending lambda suspending function type coroutine builder suspension point continuation
13. A coroutine is… an instance of suspendable computation similar to a daemon thread, but very light-weight similar to a future or promise
14. Why coroutines? threads are expensive to keep and switch your code is single threaded you’ve got lots of mutable states
15. suspend fun computation that can be suspended
16. Standard API • Language support (`suspend` keyword) • low-level basic API (stdlib: kotlin.coroutines) • high-level APIs that can be used in user code
17. Low-level API (kotlin.coroutines) • kotlin.coroutines.experimental • create/start/suspendCoroutine() • Continuation interface • @RestrictSuspension annotation • kotlin.coroutines.experimental.intrinsics • suspendCoroutineOrReturn()
18. Continuation interface Continuation<in T> {
 val context: CoroutineContext
 fun resume(value: T)
 fun resumeWithException(exception: Throwable)
 }
19. Continuation / / Kotlin suspend fun submitPost( token: Token, item: Item): Post {…} / / Java/JVM Object submitPost( Token token, Item item, Continuation<Post> cont) {…} compiler magic
20. Patterns • generators/yield: C#, Python, Scala • async/await: C#, ECMAScript, Dart • channels, select: Go • actors: Scala
21. async/await / / C# way async Task ProcessImage(String url)
 {
 var image = await LoadImage(url);
 imageView.SetImage(image);
 } / / Kotlin way fun processImage(url: String) = async(UI) {
 val image = loadImageAsync(url).await()
 imageView.setImage(image)
 }
22. Generators API in kotlin.coroutines kotlin.coroutines.experimental buildIterator() buildSequence()
23. buildSequence {
 print("Start")
 yield(1) / / suspension point
 var prev = 0; var cur = 1
 while (true) {
 val next = prev + cur print(“Next")
 yield(next) / / suspension point
 prev = cur; cur = next
 }
 print("End") / / unreachable code
 }.take(6).forEach { print(" $it ") }
 / / Output: Start 1 Next 1 Next 2 Next 3 Next 5 Next 8
24. buildSequence {
 print("Start")
 yield(1) / / suspension point
 var prev = 0; var cur = 1
 while (true) {
 val next = prev + cur print(“Next")
 yield(next) / / suspension point
 prev = cur; cur = next
 }
 print("End") / / unreachable code
 }.take(6).forEach { print(" $it ") }
 / / Output: Start 1 Next 1 Next 2 Next 3 Next 5 Next 8
25. buildSequence {
 print("Start")
 yield(1) / / suspension point
 var prev = 0; var cur = 1
 while (true) {
 val next = prev + cur print(“Next")
 yield(next) / / suspension point
 prev = cur; cur = next
 }
 print("End") / / unreachable code
 }.take(6).forEach { print(" $it ") }
 / / Output: Start 1 Next 1 Next 2 Next 3 Next 5 Next 8
26. buildSequence {
 print("Start")
 yield(1) / / suspension point
 var prev = 0; var cur = 1
 while (true) {
 val next = prev + cur print(“Next")
 yield(next) / / suspension point
 prev = cur; cur = next
 }
 print("End") / / unreachable code
 }.take(6).forEach { print(" $it ") }
 / / Output: Start 1 Next 1 Next 2 Next 3 Next 5 Next 8
27. buildSequence {
 print("Start")
 yield(1) / / suspension point
 var prev = 0; var cur = 1
 while (true) {
 val next = prev + cur print(“Next")
 yield(next) / / suspension point
 prev = cur; cur = next
 }
 print("End") / / unreachable code
 }.take(6).forEach { print(" $it ") }
 / / Output: Start 1 Next 1 Next 2 Next 3 Next 5 Next 8
28. buildSequence {
 print("Start")
 yield(1) / / suspension point
 var prev = 0; var cur = 1
 while (true) {
 val next = prev + cur print(“Next")
 yield(next) / / suspension point
 prev = cur; cur = next
 }
 print("End") / / unreachable code
 }.take(6).forEach { print(" $it ") }
 / / Output: Start 1 Next 1 Next 2 Next 3 Next 5 Next 8
29. kotlinx.coroutines Core integration Guava JDK 8 NIO Quasar reactive Reactor RxJava 1.x Reactive Streams RxJava 2.x UI Android JavaFX Swing
30. run, runBlocking for main functions and tests
31. delay like Thread.sleep(), but non-blocking
32. launch fire and forget (Job)
33. async promise returned (Deferred + await)
34. Channel transfers values between coroutines
35. produce produces a stream of values by sending them to a channel (ProducerJob)
36. actor deals with it’s mailbox (ActorJob)
37. select waits for the result of multiple suspending functions
38. Job lifecycle New Active Cancelling Completed Cancelled
39. Job states State isActive isCompleted isCancelled New - - - Active + - - Completed - + - Cancelling - - + Cancelled - + +
40. val deferred = async(CommonPool) {
 throw SomeException("I'm thrown inside a coroutine")
 }
 try {
 deferred.await() / / re-throws
 } catch (e: SomeException) {
 log(e.message)
 } Exception handling
41. WeakReference “life hack” suspend operator fun <T> WeakReference<T>.invoke(): T = suspendCoroutineOrReturn { get() ?: throw CancellationException() } val activityRef = WeakReference(this)
 launch(CommonPool) {
 activityRef().expensiveComputation()
 }
42. Demo
43. A lot more left… Coroutine dispatchers Cancellation Mutable state and concurrency UI programming Reactive streams
44. Links Andrey Breslav FAQ:
 https:/ /discuss.kotlinlang.org/t/experimental-status-of-coroutines-in-1-1-and- related-compatibility-concerns/2236 Design document (KEEP):
 https:/ /github.com/Kotlin/kotlin-coroutines/blob/master/kotlin-coroutines- informal.md Full kotlinx.coroutines API:
 http:/ /kotlin.github.io/kotlinx.coroutines Coroutines guide by Roman ELizarov:
 https:/ /github.com/Kotlin/kotlinx.coroutines/blob/master/coroutines-guide.md
45. We are hiring!
46. Thank you! @DmitriyZaitsev